Semiconductor device

ABSTRACT

An oxide semiconductor transistor comprising an oxide semiconductor layer with high conductivity is provided. A semiconductor device including an oxide semiconductor layer comprising an oxide containing indium, gallium, and zinc (IGZO) and a particle of indium oxide; a gate electrode overlapping with a channel formation region in the oxide semiconductor layer with a gate insulating film interposed therebetween; and a source electrode and a drain electrode overlapping with a source region and a drain region in the oxide semiconductor layer. The semiconductor device may be a top-gate oxide semiconductor transistor or a bottom-gate oxide semiconductor transistor. The oxide semiconductor layer may be formed over or below the source electrode and the drain electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One embodiment of the disclosed invention relates to a semiconductordevice.

2. Description of the Related Art

In recent years, a technique in which transistors are manufactured usingan oxide semiconductor and applied to electronic devices or opticaldevices has attracted attention. For example, Patent Document 1 andPatent Document 2 disclose a technique in which a transistor is formedusing an oxide containing indium (In), gallium (Ga), and zinc (Zn)(hereinafter called “IGZO”) as an oxide semiconductor to manufacture adisplay device using the transistor.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2007-123861

[Patent Document 2] Japanese Published Patent Application No.2007-096055

SUMMARY OF THE INVENTION

IGZO has low conductivity. An oxide semiconductor transistor in whichIGZO is used for an active layer might have a low on-state current, forexample.

In view of the above, an object of one embodiment of the disclosedinvention is to provide an oxide semiconductor transistor including anoxide semiconductor layer with high conductivity.

One embodiment of the disclosed invention relates to a semiconductordevice including an oxide semiconductor layer comprising an oxidecontaining indium, gallium, and zinc (IGZO) and a particle of indiumoxide; a gate electrode overlapping with a channel formation region inthe oxide semiconductor layer with a gate insulating film interposedtherebetween; and a source electrode and a drain electrode overlappingwith a source region and a drain region in the oxide semiconductorlayer.

According to one embodiment of the disclosed invention, an oxidesemiconductor layer comprises IGZO in which a crystal of indium oxide(In₂O₃) formed by bonding indium and oxygen contained in IGZO togetherexists as a particle.

Indium oxide whose energy gap is 2.8 eV is a semiconductor which isclose to an insulator in characteristics. When indium and oxygenincluded in IGZO form a particle of indium oxide which is close to aninsulator in characteristics, electric charge in IGZO is polarized. Thatis, in IGZO, the particle of indium oxide has characteristics close tothose of an insulator, while a portion from which oxygen and indium areextracted to form the particle of indium oxide has higher conductivitythan the other portions. In addition, particles of indium oxide aredispersed in the oxide semiconductor layer; for this reason, themovement of carriers is not interrupted. Thus, the oxide semiconductorlayer comprising IGZO in which the particle of indium oxide exists hashigh conductivity.

By using the oxide semiconductor layer with high conductivity as anoxide semiconductor layer of an oxide semiconductor transistor, thecarrier mobility increases and the on-state current of the oxidesemiconductor transistor increases.

One embodiment of the disclosed invention relates to a semiconductordevice including: a gate electrode; a gate insulating film covering thegate electrode; an oxide semiconductor layer comprising an oxidecontaining indium, gallium, and zinc and a particle of indium oxide, andoverlapping with the gate electrode with the gate insulating filminterposed therebetween; and a source electrode and a drain electrodeover a source region and a drain region in the oxide semiconductorlayer.

One embodiment of the disclosed invention relates to a semiconductordevice including: a gate electrode; a gate insulating film covering thegate electrode; a source electrode and a drain electrode over the gateinsulating film; and an oxide semiconductor layer comprising an oxidecontaining indium, gallium, and zinc and a particle of indium oxide. Theoxide semiconductor layer is located over the gate electrode with thegate insulating film interposed therebetween, and is located over thesource electrode and the drain electrode.

One embodiment of the disclosed invention relates to a semiconductordevice including: an oxide semiconductor layer comprising an oxidecontaining indium, gallium, and zinc and a particle of indium oxide; asource electrode and a drain electrode over a source region and a drainregion in the oxide semiconductor layer; a gate insulating film coveringthe oxide semiconductor layer, the source electrode and the drainelectrode; and a gate electrode over a channel formation region in theoxide semiconductor layer with the gate insulating film interposedtherebetween.

One embodiment of the disclosed invention relates to a semiconductordevice including: a source electrode and a drain electrode; an oxidesemiconductor layer over the source electrode and the drain electrode,which comprises an oxide containing indium, gallium, and zinc and aparticle of indium oxide, and includes a source region and a drainregion overlapping with the source electrode and the drain electrode; agate insulating film covering the oxide semiconductor layer; and a gateelectrode over a channel formation region in the oxide semiconductorlayer with the gate insulating film interposed therebetween.

According to one embodiment of the disclosed invention, an oxidesemiconductor transistor including an oxide semiconductor layer withhigh conductivity can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross-sectional views of semiconductor devices;

FIGS. 2A and 2B are cross-sectional views of semiconductor devices;

FIG. 3 is a TEM photograph of a cross section of an oxide semiconductorlayer;

FIG. 4 shows a result of TEM-FFT analysis of an oxide semiconductorlayer;

FIG. 5 shows a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor;

FIG. 6 shows a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor;

FIG. 7 shows a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor;

FIG. 8 shows a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor;

FIG. 9 shows a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor;

FIG. 10 shows a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor;

FIG. 11 shows a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor; and

FIG. 12 shows a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment of the invention disclosed in this specification will behereinafter described with reference to the accompanying drawings. Notethat the invention disclosed in this specification can be carried out ina variety of different modes, and it is easily understood by thoseskilled in the art that the modes and details of the invention disclosedin this specification can be changed in various ways without departingfrom the spirit and scope thereof. Therefore, the present invention isnot construed as being limited to description of the embodiment. Notethat, in the drawings hereinafter shown, the same portions or portionshaving similar functions are denoted by the same reference numerals, andrepeated description thereof will be omitted.

Note that in the invention disclosed in this specification, asemiconductor device refers to an element or a device which functions byutilizing a semiconductor and includes, in its category, an electricdevice including an electronic circuit, a display device, alight-emitting device, and the like and an electronic appliance on whichthe electric device is mounted.

Note that the position, size, range, or the like of each structure shownin the drawings and the like is not accurately represented in some casesfor easy understanding. Therefore, the disclosed invention is notnecessarily limited to the position, size, range, or the like asdisclosed in the drawings and the like.

In this specification and the like, ordinal numbers such as “first”,“second”, and “third” are used in order to avoid confusion amongcomponents, and the terms do not mean limitation of the number ofcomponents.

FIGS. 1A and 1B and FIGS. 2A and 2B illustrate structures of oxidesemiconductor transistors according to this embodiment.

An oxide semiconductor transistor 101 illustrated in FIG. 1A includes abase insulating film 102 over a substrate 100; a gate electrode 103 overthe base insulating film 102; a gate insulating film 104 covering thebase insulating film 102 and the gate electrode 103; an oxidesemiconductor layer 105 overlapping with the gate electrode 103 with thegate insulating film 104 interposed therebetween and functioning as anactive layer; and an electrode 106 a and an electrode 106 b over asource region and a drain region in the oxide semiconductor layer 105and functioning as a source electrode and a drain electrode.

The oxide semiconductor transistor 101 illustrated in FIG. 1A is abottom-gate transistor in which the gate electrode 103 is formed belowthe oxide semiconductor layer 105, and is also a top-contact transistorin which the electrode 106 a and the electrode 106 b functioning as thesource electrode and the drain electrode are formed over the oxidesemiconductor layer 105.

In the oxide semiconductor transistor 101 illustrated in FIG. 1A, aregion of the oxide semiconductor layer 105, which is over the gateelectrode 103, that is, a channel formation region, has a smallerthickness than the other regions thereof due to the influence of etchingand the like. The transistor whose channel formation region is thin isreferred to as a channel-etch transistor. The oxide semiconductortransistor 101 illustrated in FIG. 1A may be not only the channel-etchtransistor, but also a channel-protective transistor which has aprotective insulating film over a channel formation region.

An oxide semiconductor transistor 111 illustrated in FIG. 1B includes abase insulating film 112 over a substrate 110; a gate electrode 113 overthe base insulating film 112; a gate insulating film 114 covering thebase insulating film 112 and the gate electrode 113; an electrode 116 aand an electrode 116 b over the gate insulating film 114 and functioningas a source electrode and a drain electrode; and an oxide semiconductorlayer 115. The oxide semiconductor layer 115 functioning as an activelayer is located over the gate electrode 113 with the gate insulatingfilm 114 interposed therebetween, and is located over the electrode 116a and the electrode 116 b functioning as the source electrode and thedrain electrode.

In FIG. 1B, the electrode 116 a and the electrode 116 b functioning as asource electrode and a drain electrode do not overlap with the gateelectrode 113. If needed, portions of the electrode 116 a and theelectrode 116 b may overlap with the gate electrode 113 with the gateinsulating film 114 interposed therebetween.

The oxide semiconductor transistor 111 illustrated in FIG. 1B is abottom-gate transistor in which the gate electrode 113 is formed belowthe oxide semiconductor layer 115, and is also a bottom-contacttransistor in which the electrode 116 a and the electrode 116 bfunctioning as the source electrode and the drain electrode are formedbelow portions of the oxide semiconductor layer 115.

An oxide semiconductor transistor 201 illustrated in FIG. 2A includes abase insulating film 202 over a substrate 200; an oxide semiconductorlayer 203 over the base insulating film 202 and functioning as an activelayer; an electrode 204 a and an electrode 204 b over the oxidesemiconductor layer 203 and functioning as a source electrode and adrain electrode; a gate insulating film 206 over the oxide semiconductorlayer 203, the electrode 204 a, and the electrode 204 b; and a gateelectrode 207 overlapping with a channel formation region 209 in theoxide semiconductor layer 203 with the gate insulating film 206interposed therebetween.

The oxide semiconductor transistor 201 illustrated in FIG. 2A is atop-gate transistor in which the gate electrode 207 is formed over theoxide semiconductor layer 203, and is also a top-contact transistor inwhich the electrode 204 a and the electrode 204 b functioning as thesource electrode and the drain electrode are formed over the oxidesemiconductor layer 203.

A region 208 a and a region 208 b in the oxide semiconductor layer 203,which overlap with the electrode 204 a and the electrode 204 b, functionas a source region and a drain region.

In addition, a region 211 a is located between the channel formationregion 209 and the region 208 a, and a region 211 b is located betweenthe channel formation region 209 and the region 208 b. The region 211 aand the region 211 b function as offset regions.

An oxide semiconductor transistor 221 illustrated in FIG. 2B includes abase insulating film 222 over a substrate 220; an electrode 224 a and anelectrode 224 b over the base insulating film 222 and functioning as asource electrode and a drain electrode; an oxide semiconductor layer 223over the electrode 224 a and the electrode 224 b, which includes asource region and a drain region overlapping with the electrode 224 aand the electrode 224 b, and which functions as an active layer; a gateinsulating film 226 over the oxide semiconductor layer 223, theelectrode 224 a and the electrode 224 b; and a gate electrode 227overlapping with a channel formation region 229 in the oxidesemiconductor layer 223 with the gate insulating film 226 interposedtherebetween.

In FIG. 2B, the electrode 224 a and the electrode 224 b functioning as asource electrode and a drain electrode do not overlap with the gateelectrode 227. If needed, portions of the electrode 224 a and theelectrode 224 b may overlap with the gate electrode 227 with the oxidesemiconductor layer 223 and the gate insulating film 226 interposedtherebetween.

The oxide semiconductor transistor 221 illustrated in FIG. 2B is atop-gate transistor in which the gate electrode 227 is formed over theoxide semiconductor layer 223, and is also a bottom-contact transistorin which the electrode 224 a and the electrode 224 b functioning as thesource electrode and the drain electrode are formed below the oxidesemiconductor layer 223.

A region 228 a and a region 228 b in the oxide semiconductor layer 223,which overlap with the electrode 224 a and the electrode 224 b, functionas a source region and a drain region.

In addition, a region 231 a is located between the channel formationregion 229 and the region 228 a, and a region 231 b is located betweenthe channel formation region 229 and the region 228 b. The region 231 aand the region 231 b function as offset regions.

The oxide semiconductor layer 105 in the oxide semiconductor transistor101 illustrated in FIG. 1A, the oxide semiconductor layer 115 in theoxide semiconductor transistor 111 illustrated in FIG. 1B, the oxidesemiconductor layer 203 in the oxide semiconductor transistor 201illustrated in FIG. 2A, and the oxide semiconductor layer 223 in theoxide semiconductor transistor 221 illustrated in FIG. 2B are oxidesemiconductor layers comprising IGZO and a particle of indium oxide.

As described above, the oxide semiconductor layer comprising IGZO and aparticle of indium oxide is an oxide semiconductor layer comprising IGZOin which a crystal of indium oxide (In₂O₃) formed by bonding indium andoxygen included in IGZO together exists as a particle.

Indium oxide whose energy gap is 2.8 eV is a semiconductor which isclose to an insulator in characteristics. When indium and oxygencontained in IGZO form a particle of indium oxide which is close to aninsulator in characteristics, the distribution of an electric charge inIGZO becomes uneven. That is, in IGZO, the particle of indium oxide hascharacteristics close to those of an insulator, while a portion fromwhich oxygen and indium are extracted to form the particle of indiumoxide has higher conductivity than the other portions. In addition, theparticle of indium oxide is dispersed in the oxide semiconductor layer;for this reason, the movement of carriers is not interrupted. Thus, theoxide semiconductor layer comprising IGZO in which the particle ofindium oxide exists has high conductivity.

Therefore, an oxide semiconductor transistor including the oxidesemiconductor layer comprising IGZO and a particle of indium oxide hashigh conductivity. The oxide semiconductor transistor with highconductivity has an advantage of having a high on-state current, forexample.

FIG. 3 is a TEM photograph of a cross section of an oxide semiconductorlayer comprising IGZO and a particle used in this embodiment.

The oxide semiconductor layer comprising IGZO and a particle shown inFIG. 3 was formed at a substrate temperature of 250° C. by a sputteringmethod.

Upon analyzing the particle with a TEM-FFT (Transmission ElectronMicroscopy-Fast Fourier Transform), it turns out that the particle isindium oxide. The following shows that the particle is indium oxide.

The TEM-FFT can Fourier transform the pattern of an obtained latticeimage and thereby analyze the spot position of the pattern, and cananalyze an interplanar spacing in crystal and a crystal planeorientation.

In this embodiment, a particle in an oxide semiconductor layer wasanalyzed with the TEM-FFT, and an interplanar spacing in crystal wasobtained. The result was such that the d-value of the particle in theoxide semiconductor layer was A: 0.501 nm, B: 0.265 nm, and C: 0.302 nm(see FIG. 4). Since the d-value of indium oxide (In₂O₃) is A: 0.506 nm,B: 0.270 nm, and C: 0.320 nm, it is proved that a component of theparticle is indium oxide (In₂O₃).

FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and FIG. 12each show a relation between a drain current (Id) and a gate voltage(Vg) of an oxide semiconductor transistor using an oxide semiconductorlayer of this embodiment.

The oxide semiconductor transistors used in the measurement of FIG. 5,FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and FIG. 12 are thebottom-gate top-contact oxide semiconductor transistors 101 shown inFIG. 1A. In the oxide semiconductor transistor 101 used in themeasurement of FIG. 5, the base insulating film 102 is a stacked-layerfilm in which a silicon oxynitride film with a film thickness of 150 nmis stacked over a silicon nitride film with a film thickness of 100 nm.The gate electrode 103 is a tungsten (W) film with a film thickness of100 nm. The gate insulating film 104 is a silicon nitride filmcontaining oxygen with a film thickness of 100 nm.

The oxide semiconductor layers 105 were formed to have a film thicknessof 35 nm under the following conditions: the film formation pressure was0.3 Pa, the film formation power was 9 kW (AC), the flow rate ratio ofoxygen (O₂) to argon was set to 50%, and the substrate temperature was150° C. After the film formation was performed under above conditions,the oxide semiconductor layers of FIG. 5, FIG. 7, FIG. 9, and FIG. 11were baked at 350° C. for one hour in a nitrogen atmosphere, and then,were baked at 350° C. for one hour in an atmosphere containing nitrogenand oxygen, and the oxide semiconductor layers of FIG. 6, FIG. 8, FIG.10, and FIG. 12 were baked at 450° C. for one hour in a nitrogenatmosphere, and then, were baked at 450° C. for one hour in anatmosphere containing nitrogen and oxygen. These oxide semiconductorlayers were used as the oxide semiconductor layers 105 in the respectivemeasurements.

An electrode 106 a and an electrode 106 b were formed using astacked-layer film of a titanium film with a film thickness of 100 nm,an aluminum film with a film thickness of 400 nm, and a titanium filmwith a film thickness of 100 nm.

The oxide semiconductor transistors were made to have a channel length Lof 3 μm and a channel width W of 3 μm in FIG. 5 and FIG. 6, to have achannel length L of 3 μm and a channel width W of 50 μm in FIG. 7 andFIG. 8, to have a channel length L of 6 μm and a channel width W of 50μm in FIG. 9 and FIG. 10, and to have a channel length L of 10 μm and achannel width W of 50 μm in FIG. 11 and FIG. 12.

As an interlayer insulating film (not illustrated), a silicon oxide filmof 400 nm in thickness and a photosensitive acrylic resin film of 1500nm in thickness were formed to cover the oxide semiconductor transistor101.

Finally, baking was performed at 250° C. for one hour in a nitrogenatmosphere.

As shown in FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11,and FIG. 12, while there are some variations in the on-state current,the oxide semiconductor transistors of FIG. 5, FIG. 6, FIG. 7, FIG. 8,FIG. 9, FIG. 10, FIG. 11, and FIG. 12 each have a high on-state current.According to this embodiment, a favorable oxide semiconductor transistorwhose on-state current is high can be obtained.

This application is based on Japanese Patent Application serial no.2011-178799 filed with Japan Patent Office on Aug. 18, 2011, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: a gateelectrode; a gate insulating film covering the gate electrode; an oxidesemiconductor layer comprising an oxide containing indium, gallium, andzinc and including a particle of indium oxide represented by In₂O₃,wherein the oxide semiconductor layer overlaps with the gate electrodewith the gate insulating film interposed therebetween; and a sourceelectrode and a drain electrode over a source region and a drain regionin the oxide semiconductor layer, wherein the particle has a wedgeshape.
 2. The semiconductor device according to claim 1, wherein theoxide semiconductor layer is included in a channel-etch transistor. 3.The semiconductor device according to claim 1, further comprising asubstrate and a base insulating film below the gate electrode.
 4. Thesemiconductor device according to claim 1, wherein a tip of the wedgeshape is in a direction apart from a top surface of the oxidesemiconductor layer.
 5. A semiconductor device comprising: a gateelectrode over a substrate; an oxide semiconductor layer including achannel formation region, a source region, and a drain region, thechannel formation region being adjacent to the gate electrode with agate insulating film interposed therebetween; and a source electrode anda drain electrode being in contact with the source region and the drainregion, wherein the oxide semiconductor layer comprises an oxidecontaining indium, gallium, and zinc and includes a particle of indiumoxide represented by In₂O₃, wherein the oxide semiconductor layerincludes: a first portion containing indium, gallium, zinc and oxygen;and a second portion, wherein a density of indium in the second portionis lower than a density of indium in the first portion, wherein adensity of oxygen in the second portion is lower than a density ofoxygen in the first portion, wherein the second portion has higherconductivity than other portions of the oxide semiconductor layer, andwherein the particle has a wedge shape.
 6. The semiconductor deviceaccording to claim 5, further comprising a base insulating film on thesubstrate.
 7. The semiconductor device according to claim 5, wherein theoxide semiconductor layer covers the gate electrode.
 8. Thesemiconductor device according to claim 5, wherein the source electrodeand the drain electrode are provided on the source region and the drainregion, respectively.
 9. The semiconductor device according to claim 5,wherein a tip of the wedge shape is in a direction apart from a topsurface of the oxide semiconductor layer.
 10. A semiconductor devicecomprising: a gate electrode over a substrate; an oxide semiconductorlayer including a channel formation region, a source region, and a drainregion, the channel formation region being adjacent to the gateelectrode with a gate insulating film interposed therebetween; and asource electrode and a drain electrode being in electrical contact withthe source region and the drain region, wherein the oxide semiconductorlayer comprises an oxide containing indium, gallium, and zinc andincludes a particle of indium oxide, wherein the oxide semiconductorlayer includes: a first portion containing indium, gallium, zinc andoxygen; and a second portion, wherein a density of indium in the secondportion is lower than a density of indium in the first portion, whereina density of oxygen in the second portion is lower than a density ofoxygen in the first portion, wherein the second portion has higherconductivity than other portions of the oxide semiconductor layer, andwherein the particle has a wedge shape.
 11. The semiconductor deviceaccording to claim 10, further comprising a base insulating film on thesubstrate.
 12. The semiconductor device according to claim 10, whereinthe oxide semiconductor layer covers the gate electrode.
 13. Thesemiconductor device according to claim 10, wherein the source electrodeand the drain electrode are provided on the source region and the drainregion, respectively.
 14. The semiconductor device according to claim10, wherein the indium oxide is represented by In₂O₃.
 15. Thesemiconductor device according to claim 10, wherein a tip of the wedgeshape is in a direction apart from a top surface of the oxidesemiconductor layer.